2,3,5-Trichloropyridine is a well known prior art compound. It is a crystalline material melting at 48.degree.-48.5.degree. C.
2,3,5-Trichloropyridine is useful as an intermediate for preparing various compounds having pesticidal activity. For example, the trichloro compound can be treated with an alkali metal hydroxide employing conventional techniques to prepare 3,5-dichloro-2-pyridinol. The pyridinol can then be reacted with a phosphorochloridate or phosphorochloridothioate to prepare toxicants useful for the control of mite, insect, bacterial and fungal organisms as taught in U.S. Pat. No. 3,244,586.
2,3,5-Trichloropyridine can be prepared by a variety of methods. Sell et al. teach reacting pyridine and phosphorus pentachloride in a sealed tube at 210.degree.-220.degree. C. J. Chem. Soc. 73, 437 (1888). Sell, J. Chem. Soc. 93, 437 (1908) suggest the chlorination of pyridine hydrochloride with chlorine gas at 115.degree.-120.degree. C. for an extended period of time. In a related process, pyridine hydrochloride is treated with liquid chlorine at 80.degree.-225.degree. C. and an HCl pressure of above 30 psig as taught in U.S. Pat. No. 3,732,230. Another method using 2-amino-3,5-dichloropyridine as a starting material is taught in British Pat. No. 1,215,387. Collins et al. J. Chem. Soc. (C), pages 167-174 (1971) teaches the preparation of 2,3,6-trichloropyridine wherein tetrachloro-4-hydrazinopyridine is reacted with cuprous oxide in hot water.
While the above prior art methods are useful in the preparation of 2,3,5-trichloropyridine in small yields on a laboratory scale, these methods are too expensive to be carried out on a commercial scale. Therefore, more practical procedures are continuing to be sought.